Golf balls containing interpenetrating polymer networks

ABSTRACT

The present invention is directed to a method of forming a golf ball that contains an interpenetrating polymer network, or IPN, which includes at least two polymeric components, in one or more of the layers. In one preferred embodiment, the present invention is directed to a method of forming an intermediate or cover layer that contains an IPN.

[0001] This is a continuation-in-part of U.S. patent application Ser.No. 09/833,667, filed on Apr. 13, 2001, now pending. This application isincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

[0002] The present invention is directed to a golf ball that contains aninterpenetrating polymer network, or “IPN,” including at least twopolymeric components. The method of forming a golf ball containing anIPN in one or more of the layers is also an aspect of the presentinvention.

BACKGROUND OF THE INVENTION

[0003] Various golf balls, golf ball layers, and methods of making golfballs are generally known in the art. The centers may be fluid-filled orsolid. Such golf balls may have a multilayer construction. Golf ballsmay have a wound layer or may be solid.

[0004] Regardless of the form of the ball, players generally seek a golfball that embodies a beneficial combination of properties, for example,such as maximum distance, which requires a high initial velocity uponimpact. Therefore, golf ball manufacturers are continually searching fornew ways in which to provide golf balls that deliver the maximumperformance for golfers of varying skill levels.

[0005] Polyurethane materials are sometimes used in golf ball layers toprovide a beneficial mix of properties. For example, U.S. Pat. Nos.3,147,324; 5,816,937; and 5,885,172 are directed to golf balls, ormethods for making such, having a polyurethane outer cover.

[0006] U.S. Pat. No. 4,123,061 teaches a golf ball made from apolyurethane prepolymer of polyether, and a curing agent, such as atrifunctional polyol, a tetrafunctional polyol, or a diamine.

[0007] U.S. Pat. No. 5,334,673 discloses the use of two categories ofpolyurethane available on the market, i.e., thermoset and thermoplasticpolyurethanes, for forming golf ball covers and, in particular,thermoset polyurethane covered golf balls made from a composition ofpolyurethane prepolymer and a slow-reacting amine curing agent and/or adifunctional glycol.

[0008] U.S. Pat. No. 3,989,568 discloses a three-component systememploying either one or two polyurethane prepolymers and one or twopolyol or fast-reacting diamine curing agents. The reactants chosen forthe system must have different rates of reactions within two or morecompeting reactions.

[0009] U.S. Pat. No. 4,123,061 discloses a golf ball made from apolyurethane prepolymer of polyether and a curing agent, such as atrifunctional polyol, a tetrafunctional polyol, or a fast-reactingdiamine curing agent.

[0010] U.S. Pat. No. 5,334,673 discloses a golf ball cover made from acomposition of a thermosetting polyurethane prepolymer and aslow-reacting polyamine curing agent and/or a difunctional glycol.Resultant golf balls are found to have improved shear resistance and cutresistance compared to covers made from balata or SURLYN®.

[0011] U.S. Pat. No. 5,692,974 discloses methods of using cationicionomers in golf ball cover compositions. Additionally, the patentrelates to golf balls having covers and cores incorporating urethaneionomers. Improved resiliency and initial velocity are achieved by theaddition of an alkylating agent, such as tert-butyl-chloride, whichinduces ionic interactions in the polyurethane to produce cationic typeionomers.

[0012] PCT Publication WO 98/37929 discloses a composition for golf ballcovers that includes a blend of a diisocyanate/polyol prepolymer and acuring agent comprising a blend of a slow-reacting diamine and afast-reacting diamine. Improved “feel,” playability, and durabilitycharacteristics are exhibited.

[0013] U.S. Pat. No. 5,908,358 discloses a urethane golf ball covercured with a polyamine or glycol and an epoxy-containing curing agent.The urethane material in the golf ball cover also exhibits a tensilemodulus of about 5 ksi to 100 ksi. Improved shear resistancecharacteristics are seen with these golf ball covers.

[0014] Interpenetrating polymer networks, or IPNs, are occasionally usedto improve key physical properties or to aid in the compatibilization ofthe components of a polymer mixture or blend. Different kinds of IPNsand the ways in which they may be made are available from a number ofsources in the literature, such as, for example, in Advances inInterpenetrating Polymer Networks, Volume 4, by Frisch & Klempner, andin Interpenetrating Polymer Networks by Klempner, Sperling, & Utracki.In addition, many patents describe compositions and methods forsynthesizing various types of IPNs containing various components.

[0015] U.S. Pat. No. 5,786,426 discloses an IPN based on polyisopreneand polyurethane used for medical devices, the formation of which wasaccomplished by swelling a thermoplastic polyurethane with THF at anincreased temperature into which cis-polyisoprene was blended andperoxide initiators were dispersed for crosslinking.

[0016] U.S. Pat. No. 5,709,948 discloses a semi-IPN prepared by reactingolefinic homopolymers with epoxy resin in the presence of an epoxycurative agent, such as a triarylsulfonium hexafluorophosphate.

[0017] U.S. Pat. No. 5,674,942 discloses a homogeneous IPN having asingle glass transition temperature made by reacting a mixture of di- orpoly-amines with a di- or poly-isocyanate to form a polyurea in thepresence of acrylic ester monomers, to be polymerized with free radicalinitiators, also in the presence of tertiary amines.

[0018] U.S. Pat. No. 5,648,432 discloses a method for improving thefracture toughness, microcracking resistance, thermal and mechanicalperformance of high-temperature resistant polymers, such as polymersmade from bis-maleimides or imide-sulfones or polysulfones, polyamides,or polyimides, by dispersing them in monomers or prepolymers oflow-temperature durable polymers, such as urethane-ethers,urethane-esters, ester-esters, ether-esters, ether-amides, ester-amides,silanes, siloxanes, or diene homopolymers or copolymers.

[0019] U.S. Pat. No. 5,539,053 discloses an IPN containing a glassypolymer, such as PMMA or polyacrylates, in which acrylate monomers arepolymerized with radical initiators such as azobisisobutyronitrile(AIBN) in the presence of urethane prepolymers and polyol curativeagents.

[0020] U.S. Pat. No. 5,331,062 discloses IPNs containing epoxy polymerswith acrylate monomers or polyurethane precursors.

[0021] U.S. Pat. No. 5,306,784 discloses a tough, processable semi-IPNmade by mixing monomer precursors of polyimides having an acetylenegroup with monomer precursors of thermoplastic polyimides. Alternately,either set of the monomer precursors may be dispersed in monomerprecursors of low modulus polymers.

[0022] U.S. Pat. No. 5,241,020 discloses the preparation of a mixtureincluding at least two different compounds that react with each other inthe absence of free radical initiators and at least one monomer having acarbon-carbon double bond that polymerizes in the presence of freeradical initiators. Examples of the former component includepolyurethane or poly-epoxy precursors, while examples of the lattercomponent include acrylates, methacrylates, acrylonitriles, vinylacetates, and other vinyl monomers.

[0023] U.S. Pat. No. 5,210,109 discloses rubber-modified IPNs preparedby swelling a crosslinked polymer in monomers, oligomers, ormacromonomers of vinyl acrylates or other vinyl moieties, which are thenpolymerized.

[0024] U.S. Pat. No. 5,084,513 discloses the dissolution of apolyalkene, such as polyethylene or polypropylene, with monomers havingvinyl aromatic or acrylate-containing moieties into which a free radicalinitiator is added to polymerize the monomers.

[0025] U.S. Pat. No. 4,923,934 discloses the formation of an IPN fromthe reaction of a blocked urethane prepolymer, a polyol, and epoxyresin, and an epoxy-catalyzing agent, such as an anhydride.

[0026] Hua et al., in J. Polym. Sci., 1999, 37, 3568, disclose an IPNbased on epoxy resin and urethane acrylate formed from an epoxy-graftedpolypropylene oxide and urethane acrylate precursors.

[0027] Japanese Patent Publication Nos. JP 62-014869 and JP 62-014870disclose IPNs based on polybutadiene rubber crosslinked by vulcanizationand an ionomeric phenol-formaldehyde resin network, which IPNs are usedin solid golf ball centers.

[0028] U.S. Pat. Nos. 5,542,677; 5,591,803; and 6,100,336 disclose golfball cover compositions containing blends of neutralized carboxylicacid-containing polymers with ethylene-alkyl acrylate copolymers. Thesepatents suggest that the neutralization of the carboxylicacid-containing polymer, thus forming an ionomer, in the presence of theethylene-alkyl acrylate copolymer may result in an IPN or alternatelymay cause dynamic vulcanization.

[0029] It is desirable to improve the compatibility, as well as thethermal and mechanical properties, of polymers and/or polymer blends inthe core or any layer disposed therearound in golf ball applications.

SUMMARY OF THE INVENTION

[0030] The present invention relates to an interpenetrating polymernetwork in a golf ball. In particular, the present invention relates toa method of forming a portion of a golf ball comprising the steps ofproviding at least a first polymeric component and a second polymericcomponent, each polymeric component comprising at least one monomer,oligomer, prepolymer, or a combination thereof; sufficientlypolymerizing each polymeric component sequentially or simultaneously toform a polymer or polymer network; crosslinking each polymer or polymernetwork to the other polymer or polymer network to form aninterpenetrating polymer network (“IPN”); and forming the IPN into theportion of the golf ball, wherein each polymeric component of themixture is polymerized by exposing the mixture to at least one energysource, at least one initiator, or a combination thereof for a timesufficient to polymerize said polymeric component.

[0031] In another embodiment, the at least one energy source is selectedfrom the group consisting of microwave radiation, infrared radiation,visible radiation, ultraviolet radiation, x-ray radiation, gammaradiation, electron beam radiation and a combination thereof. In anotherembodiment, the at least one initiator is selected from the groupconsisting of a thermal free radical initiator, a photoinitiator, acationic initiator, and a mixture thereof.

[0032] In a preferred embodiment, the thermal free radical initiator isselected from the group consisting of an azo compound, a peroxide, apersulfate, a redox initiator, and mixtures thereof. In anotherpreferred embodiment, the photoinitiator is selected from the groupconsisting of a peroxide, an azo compound, quinine, benzophenone,nitroso compound, acyl halide, hydrazone, a mercapto compound, apyrylium compound, a triacylimidazole, an organophosphorus compounds, abisimidazole, a chloroalkyltriazine, a benzoate, a benzoyl compound, abenzoin ether, a benzil ketal, a thioxanthone, an acetophenonederivative, a ketone, a metallocene, a hexafluorophosphate salt, asulfonium salt, a diacrylate, a polyol, a pyrollidone, and mixturesthereof. In yet another preferred embodiment, the cationic initiator isselected from the group consisting of a Group IA organo compound, GroupIIA organo compound, aryl sulfonium salt, hexafluorometallic salt,Bronsted acid, Lewis acid, and mixtures thereof. Typically, theinitiator is present in an amount of greater than about 0.1 parts perhundred of total polymer component. Preferably, the initiator is presentin an amount from about 0.1 to about 15 parts per hundred of totalpolymer component.

[0033] In one embodiment, the polymerization of each polymeric componentis subsequent or simultaneous with the crosslinking of each polymer orpolymer network to the other polymer or polymer network. In anotherembodiment, the first polymeric component is polymerized in the presenceor absence of at least a second polymeric component to form a firstpolymer or first polymer network. In yet another embodiment, the secondpolymeric component is polymerized in the presence of the firstpolymeric component or the first polymer or first polymer network toform a second polymer or second polymer network. In another embodiment,crosslinking of the first polymer or first polymer network to the secondpolymer or second polymer network occurs subsequently or simultaneouslywith the polymerization of the second polymeric component to form thesecond polymer or second polymer network. In yet another embodiment, thepolymerization of each polymeric component and the crosslinking of eachpolymer or polymer network to the other polymer or polymer networkoccurs simultaneously to form an IPN.

[0034] In one embodiment, the first polymeric component and the secondpolymeric component include monomeric, oligomeric or prepolymericprecursors of vinyl resins; polyolefins; polyurethanes; polyureas;polyamides; polyamide/polyurethane copolymers, polyamide/polyureacopolymers, epoxy-end-capped polyurethanes, epoxy-end-capped polyureas,polyamide/polyurethane ionomers, polyamide/polyurea ionomers, acrylicresins; olefinic rubbers; polyphenylene oxide resins; polyesters; blendsof vulcanized, unvulcanized or non-vulcanizable rubbers withpolyethylene, polypropylene, polyacetal, nylon, polyesters, or celluloseesters; or polymers or copolymers possessing epoxy-containing, orpost-polymerization epoxy-functionalized repeat units.

[0035] In a preferred embodiment, the method further comprises providinga golf ball center; and disposing the IPN about the center to provide aportion of the golf ball. In another embodiment, the IPN is included inan intermediate layer disposed about the center. In another embodiment,the IPN is included in a cover layer disposed about the center.

[0036] The present invention is also directed to a method of forming aportion of a golf ball comprising the steps of providing a firstpolymeric component comprising at least one monomer, oligomer,prepolymer, or a combination thereof; sufficiently polymerizing thefirst polymer component to form a first polymer or first polymernetwork; providing a second polymeric component comprising at least onemonomer, oligomer, prepolymer, or a combination thereof; sufficientlypolymerizing the second polymer component to form a second polymer orsecond polymer; and crosslinking the first polymer or first polymernetwork with the second polymer or second polymer network to form anIPN.

[0037] In one embodiment, the first polymeric component is polymerizedby exposing the first polymeric component to a first energy source, afirst initiator, or a combination thereof for a time sufficient topolymerize the first polymeric component. In a preferred embodiment, thefirst energy source is selected from the group consisting of microwaveradiation, infrared radiation, visible radiation, ultraviolet radiation,x-ray radiation, gamma radiation, electron beam radiation and acombination thereof. In another preferred embodiment, the firstinitiator is selected from the group consisting of a thermal freeradical initiator, a photoinitiator, a cationic initiator, and a mixturethereof. In one embodiment, the first initiator is present in an amountof greater than about 0.01 parts per hundred of the first polymericcomponent. In a preferred embodiment, the initiator is present in anamount from about 0.01 to about 15 parts per hundred of total polymercomponent.

[0038] In another embodiment, the second polymeric component ispolymerized by exposing the second polymeric component to a secondenergy source, a second initiator, or a combination thereof for a timesufficient to polymerize the second polymeric component. In a preferredembodiment, the second energy source is selected from the groupconsisting of microwave radiation, infrared radiation, visibleradiation, ultraviolet radiation, x-ray radiation, gamma radiation,electron beam radiation and a combination thereof. In a more preferredembodiment, the second energy source is electron beam radiation.

[0039] In another preferred embodiment, the second initiator is selectedfrom the group consisting of a thermal free radical initiator, aphotoinitiator, a cationic initiator, and a mixture thereof. In oneembodiment, the second initiator is present in an amount of greater thanabout 0.01 parts per hundred of the first polymeric component. In apreferred embodiment, the initiator is present in an amount from about0.01 to about 15 parts per hundred of total polymer component.

[0040] In one embodiment, the first polymeric component is polymerizedin the presence or absence of at least a second polymeric component toform a first polymer or first polymer network. In another embodiment,the second polymeric component is polymerized in the presence of thefirst polymeric component or the first polymer or first polymer networkto form a second polymer or second polymer network. In yet anotherembodiment, crosslinking of the first polymer or first polymer networkto the second polymer or second polymer network occurs subsequently orsimultaneously with the polymerization of the second polymeric componentto form the second polymer or second polymer network.

[0041] In one embodiment, the first polymeric component and the secondpolymeric component comprise monomeric, oligomeric or prepolymericprecursors of vinyl resins; polyolefins; polyurethanes; polyureas;polyamides; acrylic resins; olefinic rubbers; polyphenylene oxideresins; polyesters; blends of vulcanized, unvulcanized ornon-vulcanizable rubbers with polyethylene, polypropylene, polyacetal,nylon, polyesters, or cellulose esters; or polymers or copolymerspossessing epoxy-containing, or post-polymerization epoxy-functionalizedrepeat units.

[0042] In one embodiment, the portion of the golf ball formed from theIPN is a core, intermediate layer or cover layer. In a preferredembodiment, the method further comprises providing a golf ball center;and disposing the IPN about the center to provide a portion of the golfball. In a more preferred embodiment, the IPN is included in anintermediate layer disposed about the center. In another more preferredembodiment, the IPN is included in a cover layer disposed about thecenter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Further features and advantages of the invention can beascertained from the following detailed description that is provided inconnection with the drawings described below:

[0044]FIG. 1 illustrates a golf ball including a center and a coverlayer disposed over the center, in which at least one of the center orthe cover layer includes an IPN.

[0045]FIG. 2 illustrates a multi-layer golf ball including a center, anintermediate layer disposed over the center, and a cover layer disposedover the intermediate layer, in which at least one part of the golf ballincludes an IPN.

[0046]FIG. 3 illustrates a multi-layer golf ball including a core, anintermediate layer, and a cover layer disposed over the core, in whichat least one part of the golf ball includes an IPN.

[0047] Definitions

[0048] With respect to the present invention, all percentages are weightpercentages unless otherwise indicated.

[0049] As used herein, the term “about” should be understood to modifyeither one or both numbers in a range of values.

[0050] As used herein, the term “golf equipment” includes any type ofequipment used in connection with golf, including, but not limited to,golf clubs (i.e., putters, drivers, and wedges) and club attachments,additions, or modifications, such as striking face inserts; golf clubcomponents (e.g., shafts, hosels, and grips); golf club vibrationdamping devices; golf gloves; golf shoes; and any portion of the aboveitems. For the purposes of this invention, golf equipment does notinclude golf balls.

[0051] As used herein, the term “fluid” includes a liquid, a paste, agel, a gas, or any combination thereof. A “fluid-filled” golf ballcenter or core according to the invention also includes a hollow centeror core.

[0052] In the context of the present invention, the phrase“substantially free of” an item means that there is less than about 5%,preferably less than about 2%, more preferably less than about 1% ofthat item present. Most preferably, it means that the item is completelyfree of that item.

[0053] In the context of the present invention, the term “prepolymer”refers generally to a macromonomer or partially polymerized materialformed by the reaction product of at least two components, each having afunctionality that is reactive with at least one other component underthe appropriate circumstances, which macromonomer or partiallypolymerized material can be subsequently reacted with at least one othercomponent (which may be the same as one of the at least two componentsor different) to form a polymer. In particular, a “prepolymer” may referto a material containing at least one isocyanate-containing componentand at least one isocyanate-reactive component, for example, such as apolyol, a polyamine, an epoxy-containing compound, or a mixture thereof.Alternatively, “prepolymers” according to the present invention may notinclude an isocyanate-containing component.

[0054] In the context of the present invention, a component that has a“substantial lack of” an item should be understood to have less thanabout 20%, preferably to have less than about 10%, more preferably to besubstantially free of that item.

[0055] As used herein with regard to golf ball properties, the term“compression” refers to Atti compression, which is defined as thedeflection of an object or material relative to the deflection of acalibrated spring, as measured with an Atti Compression Gauge, that iscommercially available from Atti Engineering Corp. of Union City, N.J.Atti compression is typically used to measure the compression of a golfball. When the Atti Gauge is used to measure cores having a diameter ofless than 1.680 inches, it should be understood that a metallic or othersuitable shim is used to make the measured object 1.680 inches indiameter.

DETAILED DESCRIPTION OF THE INVENTION

[0056] The present invention relates to one-piece golf balls, two-piecegolf balls, or multilayer golf balls having a center, at least oneintermediate layer disposed concentrically adjacent to the center, and acover. The invention also relates to golf balls having a double core, amulti-layer core, a double cover, a multi-layer cover or more than oneintermediate layer.

[0057] It has now been discovered that golf balls including aninterpenetrating polymer network, or IPN, including at least twopolymeric components can advantageously provide improved golf balls. Aninterpenetrating polymer network useful for the present invention mayinclude two or more different polymers or polymer networks and canencompass any one or more of the different types of IPNs listed anddescribed below, which may overlap:

[0058] (1) Sequential interpenetrating polymer networks, in whichmonomers or prepolymers for synthesizing one polymer or a polymernetwork are polymerized in the presence of another polymer or polymernetwork. These networks may have been synthesized in the presence ofmonomers or prepolymers of the one polymer or polymer network, which mayhave been interspersed with the other polymer or polymer network afterits formation or cross-linking;

[0059] (2) Simultaneous interpenetrating polymer networks, in whichmonomers or prepolymers of two or more polymers or polymer networks aremixed together and polymerized and/or crosslinked simultaneously, suchthat the reactions of the two polymer networks do not substantiallyinterfere with each other;

[0060] (3) Grafted interpenetrating polymer networks, in which the twoor more polymers or polymer networks are formed such that elements ofthe one polymer or polymer network are occasionally attached orcovalently or ionically bonded to elements of an/the other polymer(s) orpolymer network(s);

[0061] (4) Semi-IPNs, in which one polymer is cross-linked to form anetwork while another polymer is not; the polymerization or crosslinkingreactions of the one polymer may occur in the presence of one or moresets of other monomers, prepolymers, or polymers, or the composition maybe formed by introducing the one or more sets of other monomers,prepolymers, or polymers to the one polymer or polymer network, forexample, by simple mixing, by solublizing the mixture, e.g., in thepresence of a removable solvent, or by swelling the other in the one;

[0062] (5) Full, or “true,” interpenetrating polymer networks, in whichtwo or more polymers or sets of prepolymers or monomers are crosslinked(and thus polymerized) to form two or more interpenetrating crosslinkednetworks made, for example, either simultaneously or sequentially, suchthat the reactions of the two polymer networks do not substantiallyinterfere with each other;

[0063] (6) Homo-IPNs, in which one set of prepolymers or polymers can befurther polymerized, if necessary, and simultaneously or subsequentlycrosslinked with two or more different, independent crosslinking agents,which do not react with each other, in order to form two or moreinterpenetrating polymer networks;

[0064] (7) Gradient interpenetrating polymer networks, in which eithersome aspect of the composition, frequently the functionality, thecopolymer content, or the crosslink density of one or more other polymernetworks gradually vary from location to location within some, or each,other interpenetrating polymer network(s), especially on a macroscopiclevel;

[0065] (8) Thermoplastic interpenetrating polymer networks, in which thecrosslinks in at least one of the polymer systems involve physicalcrosslinks, e.g., such as very strong hydrogen-bonding or the presenceof crystalline or glassy regions or phases within the network or system,instead of chemical or covalent bonds or crosslinks; and

[0066] (9) Latex interpenetrating polymer networks, in which at leastone polymer or set of prepolymers or monomers are in the form oflattices, frequently (though not exclusively) in a core-shell type ofmorphology, which form an interpenetrating polymer network when dried,for example, as a coating on a substrate (if multiple polymers or setsof prepolymers or monomers are in the form of lattices, this issometimes called an “interpenetrating elastomer network,” or IEN).

[0067] It should be understood that an interpenetrating polymer networkaccording to the invention should not include a copolymer network. Theterm “copolymer network,” as used herein, can be defined as a singlepolymer network formed from two or more different types of monomers,oligomers, precursor packages, or polymers, during which networkformation: a) the crosslinking reaction(s) result(s) in the differenttypes of polymers, oligomers, or precursors being sufficientlyinter-crosslinked, i.e., the polymers, oligomers, or precursors of oneor more types are connected to polymers, oligomers, or precursors of theother different types, such that effectively one crosslinked networkconnecting all the different monomers, oligomers, precursors, orpolymers is formed; b) the contemporaneous or consecutive polymerizationreaction(s) of all the different types of monomers, oligomers, orprecursors result(s) in two or more different types of copolymers, whichmay themselves be oligomeric or polymeric and may be precursors to(an)other type(s) of copolymer(s), and which may then undergointer-crosslinking reaction(s), as in a), between the different types ofcopolymers; c) the contemporaneous or consecutive polymerizationreaction(s) of all the different types of monomers, oligomers, orprecursors result(s) in a single type of copolymer, which may itself beoligomeric or polymeric and may be a precursor to another type ofcopolymer, and which may then undergo a sufficient intra-crosslinkingreaction, i.e., the copolymer chains of the single type are connected toother copolymer chains of the same type, such that effectively a singlecrosslinked network connecting copolymer chains is formed; or d) anycombination thereof.

[0068] A grafted IPN is distinguishable from a copolymer network, inthat the inter-crosslinking of a grafted IPN is only occasional,resulting in relatively few cross-type polymer linkages, while theinter-crosslinking of a copolymer network occurs relatively frequently,resulting in a relatively large amount of cross-type polymer linkages.As a result, the copolymer network is effectively a single copolymernetwork, while the grafted IPN according to the invention may be lightlyinter-crosslinked but is effectively a combination of at least two,preferably co-continuous, polymer networks. Preferably, grafted IPNsaccording to the invention have a substantial lack of cross-type polymerlinkages, or inter-crosslinking. In one embodiment, a layer containing agradient IPN according to the invention has a flexural modulus belowabout 5 ksi.

[0069] With the exception of grafted IPNs above, all forms ofcrosslinking recited in the descriptions of interpenetrating polymernetworks above should hereby be understood to be intra-crosslinks, orsame-type polymer linkages, i.e., crosslinks between polymer chains madefrom the same precursor package. Still, grafted IPNs predominantlycontain intra-crosslinks, but also contain a small amount ofinter-crosslinks.

[0070] It should also be understood that an interpenetrating polymernetwork according to the invention should not include a combination ofan individual polymer and a polymer network of essentially the same typeas the individual polymer, i.e., for example, a single type ofhomopolymer or copolymer, e.g., such as PMMA, that has been: a)incompletely crosslinked, e.g., such as by incorporation of anappropriate amount of diacrylate monomer; or b) incompletely orcompletely crosslinked and then blended with uncrosslinked, neat PMMA,is not considered an IPN according to the present invention, despite itspossible characterization as a semi-homo-IPN. Such a combination isconsidered a partially-crosslinked, single-polymer network or system.

[0071] Generally, IPNs improve the compatibility of polymericcomponents, especially in comparison to conventional polymer blends. Inan interpenetrating polymer network of the present invention, thecompatibility can be evidenced by comparing experimentally measuredproperties, such as the relative glass transition temperatures (or thedifference between them, denoted as ΔT_(g)) or the relativecrystallinity or crystalline perfection (as represented by the areaunder the melting endotherm), if at least one component of the IPN iscrystallizable. These properties may be experimentally observed by anumber of different instruments, such as a differential scanningcalorimeter (“DSC”) or dynamic mechanical analyzer (“DMA”) or dynamicmechanical thermal analyzer (“DMTA”).

[0072] Preferably, the formation of an IPN reduces the ΔT_(g) between atleast two of the polymeric components of the IPN at least about 5%, ascompared with the ΔT_(g) between a polymer blend containing the same atleast two polymeric components. In one embodiment, the formation of anIPN reduces the ΔT_(g) between at least two of the polymeric componentsof the IPN at least about 10%. In another embodiment, the formation ofan IPN reduces the ΔT_(g) between at least two of the polymericcomponents of the IPN at least about 20%. In various other embodiments,the formation of an IPN reduces the ΔT_(g) between at least two of thepolymeric components of the IPN at least about 35%, at least about 50%,and at least about 75%. In yet another embodiment, the formation of anIPN yields only one observable T_(g) for the at least two polymericcomponents.

[0073] Alternately, in the case where at least two of the polymericcomponents of the IPN associate or interact strongly in a polymer blend,especially through hydrogen-bonding, ionic aggregation, chelation, orthe like, the formation of an IPN can increase the ΔT_(g) between the atleast two polymeric components in the IPN, in some cases at least about5%, as compared with the ΔT_(g) between a polymer blend containing thesame at least two polymeric components. In one such alternateembodiment, the formation of an IPN increases the ΔT_(g) between atleast two of the polymeric components of the IPN at least about 10%. Inanother such alternate embodiment, the formation of an IPN increases theΔT_(g) between at least two of the polymeric components of the IPN atleast about 20%.

[0074] For example, in the case of a polyurethane-epoxy polymer IPNsystem, a polymer blend containing the polyurethane and the epoxypolymer can be made in a number of ways, such as by: grinding a curedepoxy polymer into a powder; mixing the proper proportion of thepowdered epoxy polymer with the urethane precursor package components touniformly disperse the epoxy powder, but before polymerization,gelation, or solidification occurs; and shaping the mixture into asimilar shape as the IPN (e.g., a golf all or portion thereof). Thisprocedure can advantageously be used for any blend in which at least oneof the polymeric components is a thermoset material.

[0075] Preferably, the formation of an IPN reduces the absolute value ofthe area under the melting endotherm, often called ΔH_(f), of at leastone of the crystallizable polymeric components of the IPN at least about5% less than the area under the melting endotherm of a polymer blend ofthe same ratio of the at least one crystallizable polymeric component.In one embodiment, the formation of an IPN reduces ΔH_(f) of at leastone of the crystallizable polymeric components of the IPN at least about10% compared to the blend. In another embodiment, the formation of anIPN reduces ΔH_(f) of at least one of the crystallizable polymericcomponents of the IPN at least about 15% compared to the blend. Invarious other embodiments, the formation of an IPN reduces ΔH_(f) of atleast one of the crystallizable polymeric components of the IPN at leastabout 25% compared to the blend, at least about 50% compared to theblend, and at least about 75% compared to the blend. In yet anotherembodiment, the formation of an IPN results in at least one of thecrystallizable polymeric components being substantially free ofcrystallinity, as measured by ΔH_(f).

[0076] When performing DMA or DMTA experiments, ASTM D4065-95 wasfollowed in analyzing sample material responses. A heating rate of nomore than about 2° C./min was employed for these tests, and thethicknesses of the samples were kept within about 5% of the averagethickness. When performing DSC experiments to measure the glasstransition temperature, T_(g), or the melting temperature, T_(pm), ofsamples, ASTM D3418-99 was followed, in which the numerical value ofT_(g) represents the median temperature of the transition and thenumerical value of T_(pm) represents the peak extremum of the meltingendotherm. When performing DSC experiments to measure the degree ofcrystallinity or the area under the melting endotherm, ΔH_(f), ASTMD3417-99 was followed.

[0077] As is very often the case in multi-polymer blend systems, two ofthe polymeric components may be immiscible or partially miscible, suchthat phase separation occurs to a certain extent. This phase separationmay be visible to one of ordinary skill in the art (macrophaseseparation) or may only be observable through specializedcharacterization techniques designed to probe regions of less than about500 microns (microphase separation). At the meeting of the at least twophases, there is a phase boundary that defines the edge of each phase.The average size of the phases of each phase separated component can beexperimentally measured using, for example, atomic force microscopy,scanning electron microscopy, transmission electron microscopy, or otherappropriate characterization apparatus.

[0078] In a preferred embodiment, the formation of an IPN, in which twoof the polymeric components may be immiscible or partially miscible,results in an average phase size of each phase separated component thatcan be considerably less than the average phase size of each phaseseparated component in a blend of two or more of the components. In oneembodiment, the formation of an IPN results in an average phase size ofeach phase separated component being at least about 10% smaller than ablend of the two components. In another embodiment, the formation of anIPN results in an average phase size of each phase separated componentbeing at least about 20% smaller than a blend of the two components. Invarious other embodiments, the formation of an IPN results in an averagephase size of each phase separated component being at least about 35%smaller than a blend of the two components, at least about 60% smallerthan a blend of the two components, and at least about 85% smaller thana blend of the two components. In some cases, IPN formation can resultin complete miscibility of the system, resulting in no discernible phaseboundaries, while the components may have been immiscible or onlypartially miscible when in a blend.

[0079] In one embodiment, the formation of an IPN increases at least oneof the following measurable quantities: the area under the loss moduluspeak, represented by a local maximum in E″, or loss tangent peak,represented by a local maximum in tan δ; the temperature range overwhich the loss modulus or loss tangent peak extends; the full-width athalf-maximum height (FWHM) of the loss modulus or loss tangent peak; orthe number of loss modulus or loss tangent peaks over a giventemperature interval, as compared to the same value(s) measured for ablend of the same ratio of the at least two IPN components. In anotherembodiment, the formation of an IPN increases at least one of theaforementioned measurable quantities by at least about 2%, as comparedto the same value(s) measured for a blend of the same ratio of the atleast two IPN components. In yet another embodiment, the formation of anIPN increases at least one of the aforementioned measurable quantitiesby at least about 5%, as compared to the same value(s) measured for ablend of the same ratio of the at least two IPN components. In stillanother embodiment, the formation of an IPN increases at least one ofthe aforementioned measurable quantities by at least about 10%, ascompared to the same value(s) measured for a blend of the same ratio ofthe at least two IPN components. In various other embodiments, theformation of an IPN increases at least one of the aforementionedmeasurable quantities by at least about 25%, by at least about 50%, andby at least about 75%, as compared to the same value(s) measured for ablend of the same ratio of the at least two IPN components. Alternately,instead of a comparison to the value(s) measured for a blend of the sameratio of the at least two IPN components, at least one of theaforementioned measure quantities can be compared to an uncrosslinkedpolymer of one of the at least two IPN components, a crosslinked polymerof one of the at least two IPN components, a random, block, graft, orother type of copolymer of at least two of the individual polymercomponents of the IPN, a crosslinked copolymer of at least two of theindividual polymer components of the IPN, or some combination thereof.

[0080] It is also desirable for the cover, or the outermost layer of thecover if the cover has a plurality of layers, to exhibit a high shearresistance, which is manifest as the ability of a material to maintainits mechanical stability and integrity upon the application of a shearstress to that material. A “shear resistance rating” is a qualitative,or relative, scale for assessing the relative shear resistance of amaterial. The lower the shear resistance rating is, the higher the shearresistance of the material. For painted golf ball cover materials, theshear resistance rating categories from 1 to 5 are listed and describedin the table below: Description Rating No visible damage to cover orpaint 1 Paint damage only 2 Slight cover shear and/or paint damageobserved 3 Moderate cover shear; fraying; and/or slight material removed4 Extensive cover shear; heavy material removed; and/or severe 5material clumping

[0081] The shear resistance rating can be determined by using a Miya™mechanical Golf Swing Machine, commercially available from Miyamae Co.,Ltd., of Osaka, Japan, to make two hits on each of about 6 to 12substantially identical golf balls of substantially the same compositionwith either a sand wedge or a pitching wedge. First, the test conditionsare adjusted and verified so that a control golf ball having a balatacover produces a rating of 5 on the shear resistance rating scale above.Following the calibration procedure, each experimental golf ball istested and assigned a rating based upon visible manifestations of damageafter being struck. The shear resistance rating for a golf ball coverlayer of a given composition represents a numerical average of all thetested substantially identical golf balls. One alternative way to testshear resistance of a golf ball cover involves using player-testing andevaluating the results after the ball is struck multiple times withwedges and/or short irons.

[0082] In a preferred embodiment, the formation of an IPN in a layer ofa golf ball according to the present invention increases the shearresistance of the cover layer of that golf ball, preferably resulting ina decrease in the shear test rating of at least 1, more preferablyresulting in a decrease of at least 2, compared to the cover layermaterial of a conventional golf ball that is substantially free of IPNand that is made of the same components as the IPN. In that embodiment,it is preferred that the shear resistance of the cover layer of thatgolf ball has a shear test rating of at most 3, most preferably of atmost 2.

[0083] Advantageously, the formation of an IPN in a golf ball layer mayalso increase the resistance to moisture penetration of that layer. IPNformation in that layer may also provide reduction in the water vaporpermeability of a golf ball layer having an IPN therein. The reducedexposure of golf ball materials to water or water vapor helps inhibitdegradation of or maintain the mechanical and/or chemical properties ofthose materials. This is particularly true when the water or moisturecan facilitate degradation of molecular weight or mechanical propertiesof one or more components of the materials within the golf ball.

[0084] The ranges of values of several golf ball or material propertieslisted herein can vary, even outside their recited ranges, by theinclusion of IPNs according to the invention and, if necessary, byselectively varying at least one other property mentioned herein.Examples of such golf ball or material properties whose ranges can bevaried by inclusion of an IPN include, but are not limited to, tensileor flexural modulus and impact resistance.

[0085] IPNs according to the present invention include at least twoprecursor packages, which correspond to the at least two polymercomponents or networks. Each precursor package contains at least all thecompounds necessary to form one of the polymerized components of theIPN. Compounds that may be used in a precursor package include anymonomers, oligomers, or pre-polymers that are to be attached to thepolymer component by polymerization. Most notably inpolyurethane-containing systems, a chain extender component is alsoincluded to further linearly extend a pre-polymer component. Whenreferring to polymers synthesized by step-growth polymerization, itshould be understood that monomers, oligomers, and pre-polymers refer toany or all compounds with functional groups that participate in thepolymerization and are attached to the resulting step-growth homopolymeror copolymer.

[0086] Although some polymers may be formed through self-polymerization,for example, such as polystyrene from styrene monomer, when activated byheat or the appropriate energy, most chain growth polymerizationsinvolve an initiator. The choice of initiator of use in the presentinvention depends on each polymer component to be synthesized, and anyavailable initiator capable of polymerizing the selected monomers,oligomers, or pre-polymers are generally also present in a precursorpackage. Suitable initiators can include, for example, free radical,cationic initiators or ionic initiators. In cases where commerciallyavailable initiators contain inhibitors, the inhibitors may be separatedand removed from the initiator by known methods prior to use.

[0087] The amount of radiation energy needed to sufficiently initiatepolymerization, cure and/or crosslink the composition depends upon anumber of factors including, for example, the chemical identity of thecomposition and precursors, as well as the initiator, radiation sourcechosen, and length of exposure time of the polymer components to theenergy source. Thermal radiative sources include infrared and microwavesources. Conditions for thermal or heat initiated polymerizationstypically are from about 35° C. to about 300° C., preferably from about50° C. to about 200° C. and for a time of about fractions of minutes toabout thousands of minutes. Examples of thermal free radical initiatorsinclude azo compounds, peroxides, persulfates (e.g., potassiumpersulfate, sodium persulfate, and ammonium persulfate), and redoxinitiators.

[0088] If actinic radiation is utilized, such as ultraviolet or visiblelight, a photoinitiator may be utilized. Upon being exposed toultraviolet or visible light, the photoinitiator generates a freeradical source or a cationic source. This free radical source orcationic source then initiates the polymerization. In free radicalprocesses, an initiator is optional when a source of electron beamradiation, x-ray or gamma radiation energy is utilized. Thus, aninitiator may be present or absent when the energy source is electronbeam radiation, x-ray or gamma radiation energy. Gamma radiation andelectron beam radiation are useful because of their excellentpenetration at ambient temperature allows more control in the quiescentconditions. Gamma radiation and electron beam radiation are alsoadvantageous because they require minimal cooling of the cured inks (thecuring is done at ambient or room temperature), the ink are almostinstantaneously cured, obviate or reduce the need for costly ventilatingsystems, and, in the case of low power electron beam radiation, requirelow energy to cure. Additionally, curing by gamma radiation or electronbeam radiation allows the combination of several ink compositions in thesame curing cycle, which may not be possible for thermal curing becausethe different ink compositions may require different temperatures orcure times. Suitable photoinitiators include, for example, those thatabsorb in the wavelength range from about 0.001 nm to 700 nm, preferablyfrom about 100 nm to about 650 nm, more preferably from about 190 nm toabout 600 nm. Photoinitiators include peroxides, azo compounds, quinines(e.g., substituted and unsubstituted anthraquinones, camphor quinone,alkyl-camphorquinone), benzophenones (e.g., 4-methylbenzophenone,benzophenone, 4,4′-bisdimethylamine-benzophenone, 1-hydroxycyclohexylphenyl ketone), nitroso compounds, acyl halides, hydrazones, mercaptocompounds, pyrylium compounds, triacylimidazoles, organophosphoruscompounds (e.g., acylphosphine oxides,2,4,6-trimethylbenzoyldiphenylphosphine oxide), bisimidazoles,chloroalkyltriazines, benzoates (e.g., ethyl 4-(dimethylamino)benzoate),benzoyl compounds (e.g., acrylic or methacrylic[(2-alkoxy-2-phenyl-2-benzoyl)ethyl]esters, 4-benzoyl-4′-methyldiphenylsulfide, 1-benzoylcyclohexanol), benzoin ethers (e.g., substituted andunsubstituted C₁-C₈ alkyl benzoin ethers, such as benzoisobutyl ether),benzil ketals (e.g., benzyldimethyl ketal), thioxanthones (e.g.2-isopropylthioxanthone and 4-isopropylthioxanthone), acetophenonederivatives (e.g., 2,2-dimethoxy-2-phenyl-acetophenone,2,2-diethoxyacetophenone, 2,2-diacetoxyacetophenone, chlorinatedacetophenone, hydroxyacetophenone), ketones (e.g.,2-methyl-1-(4-[methylthio]phenyl)-2-(4-morpholinyl)-1-propanone,2-hydroxy-2-methyl-1-phenylpropan-1-one, 4-(2-hydroxyethoxy)phenyl2-hydroxy-2-propyl ketone,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)furan-1-one),metallocenes (e.g., Group VIII metallocenes, perfluorinateddiphenyltitanocenes), hexafluorophosphate salts (e.g.,(η⁵-cyclopentadienyl)(η⁶-isopropylphenyl)iron(II) hexafluorophosphate,triphenylsulfonium hexafluorophosphate), sulfonium salts, diacrylates(e.g., butanediol diacrylate, dipropylene glycol diacrylate, hexanedioldiacrylate, 4-(1,1-dimethylethyl)cyclohexyl acrylate, trimethylolpropanetriacrylate and tripropylene glycol diacrylate), polyols (e.g.,polyethylene glycol), pyrollidones (e.g., N-vinyl pyrollidone) andmixtures thereof. Examples of commercially available photoinitiatorsinclude, but are not limited to, Vicure 10, 30 (made by StaufferChemical), Irgacure 184, 651, 2959, 907, 369, 1700, 1800, 1850, 819(made by Chiba Specialty Chemicals), Darocurel 173 (made by EMChemical), Quantacure CTX, ITX (made by Aceto Chemical), Lucirin TPO(made by BASF). Other examples of suitable photoinitiators are describedin, for example, U.S. Pat. No. 6,500,495, the entirety of which isincorporated herein by reference.

[0089] Cationic initiators include Group IA or Group IIA organocompounds, aryl sulfonium salts, hexafluorometallic salts, Bronstedacids, Lewis acids or mixtures thereof. In particular, cationicinitiators include sec-butyllithium, n-butyllithium, other(C₁-C₁₀)alkyllithiums, aryllithiums, sulfonic acids (e.g. sulfuricacid), phosphoric acid, perchloric acid, triflic acid, BF₃, aluminumhalides (e.g., AlCl₃, AlBr₃), triarylsulfonium salts, diaryliudoniumsalts or mixtures thereof.

[0090] Peroxide and organic peroxide initiators typically are R—O—O—R₁,wherein R and R₁ are each independently selected from the groupconsisting of hydrogen, (C₁-C₂₀)alkyl, (C₁-C₂₀)alkylene,(C₁-C₂₀)alkylyne, (C₁-C₂₀)cycloalkyl, and substituted or unsubstituted(C₆-C₂₄)aryl, wherein aryl may be phenyl, naphthyl, biphenyl, thienyl orpyridyl and the aryl moiety may in each case be mono- to trisubstitutedby F, Cl, Br, I, OH, CF₃, NO₂, CN, OCF₃, O-(C₁-C₁₀)alkyl, NH₂,NH(C₁-C₆)alkyl, COOH, COO(C₁-C₆)alkyl. As used herein, “substituted”refers to additional moieties or groups that are attached to and foundin R and R₁, which includes, but are not limited to F, Cl, Br, I, OH,CF₃, NO₂, CN, OCF₃, O-(C₁-C₁₀)alkyl, NH₂, NH(C₁-C₆)alkyl, COOH,COO(C₁-C₁₀)alkyl, (C₁-C₁₀)alkyl, (C₂-C₁₀)alkenyl, (C₂-C₁₀)alkynyl,(C₁-C₁₀)alkyl-COOH, (C₁-C₁₀)alkyl-aryl, wherein aryl may be phenyl,naphthyl, biphenyl, thienyl or pyridyl and the aryl moiety may in eachcase be mono-, di- or tri-substituted by F, Cl, Br, I, OH, CF₃, NO₂, CN,OCF₃, O-(C₁-C₁₀)alkyl, NH₂, NH(C₁-C₆)alkyl, COOH, COO(C₁-C₆)alkyl.

[0091] Examples of peroxide and organic peroxide initiators include, butare not limited to, di(2-tert-butyl-peroxyisopropyl)benzene peroxide orbis(tert-butylperoxy)diisopropylbenzene,2,5-di-(tert-butylperoxy)-2,5-dimethyl hexane,n-butyl-4,4-bis(tert-butylperoxy)valerate, lauryl peroxide,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide,di-tert-butyl peroxide, di-tert-amyl peroxide, benzoyl-5-peroxide,tert-butyl hydroperoxide, benzoyl peroxide, acetyl peroxide, decanoylperoxide, dicetyl peroxydicarbonate, di(4-tert-butylcyclohexyl)peroxydicarbonate (available under the trade designation PERKADOX 16,from Akzo Chemicals, Inc., Chicago, Ill.), di(2-ethylhexyl)peroxydicarbonate, tert-butylperoxypivalate (available under the tradedesignation LUPERSOL 11, from Lucidol Division., Atochem North America,Buffalo, N.Y.) and tert-butylperoxy-2-ethylhexanoate (available underthe trade designation TRIGONOX 21-C50, from Akzo Chemicals, Inc.,Chicago, Ill.).

[0092] Azo compounds include, but are not limited to,4,4′-azobis(isobutyronitrile), 4,4′-azobis(cyanovalerate),4,4′-azobis(cyanovaleric acid),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (available under thetrade designation VAZO 33); 2,2′-azobis(2-amidinopropane)dihydrochloride (available under the trade designation VAZO 50);2,2′-azobis(2,4-dimethylvaleronitrile) (available under the tradedesignation VAZO 52); 2,2′-azobis(isobutyronitrile) (also known as AIBN,available under the trade designation VAZO 64);2,2′-azobis-2-methylbutyronitrile (available under the trade designationVAZO 67); 1,1′-azobis(1-cyclohexanecarbonitrile) (available under thetrade designation VAZO 88), all of which are available from E.I. Dupontde Nemours and Company, Wilmington, Del., and2,2′-azobis(methylisobutyrate) (available under the trade designationV-601 from Wako Pure Chemical Industries, Ltd., Osaka, Japan), and otherazo compounds.

[0093] In one embodiment, the free radical initiator is aninhibitor-containing peroxide, such as 2,6-di-tert-butylbenzoquinone,2,6-di-tert-butyl-4-methylene-2,5-cyclohexadiene-1-one,2,6-di-tert-butyl-4-hydroxybenzaldehyde,2,6-di-tert-butyl-4-isopropylphenol, 4,4′-methylenebis-(2,6-di-tert-butylphenol),1,2-bis-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane,2,3,5,6-tetramethylbenzoquinone, 2-tert-butylhydroquinone,2,2′-methylenebis-(4-methyl-6-tert-butylphenol), and the like, andmixtures thereof. The initiator, i.e., photoinitiator, free-radicalinitiator or cationic initiator, is generally present in an amountsufficient to initiate a polymerization resulting in a polymer having anumber average molecular weight suitable for use in golf balls, which istypically from about 1,000 to about 10,000,000 grams/mole.Alternatively, the initiator (i.e., photoinitiator, free radicalinitiator or cationic initiator) may be present in an amount greaterthan about 0.01 parts per hundred of the polymer component, preferablyfrom about 0.01 to about 15 parts per hundred of the polymer component,and more preferably from about 0.1 to about 10 parts per hundred of thepolymer component, and most preferably from about 0.2 to about 5 partsper hundred of the total polymer component. It should be furtherunderstood that heat often facilitates initiation of the generation offree radicals in the aforementioned compounds.

[0094] In another embodiment, the initiator is selected to suit or matchthe radiation cure technique that is used to initiate the polymerizationprocess. For example, a photoinitiator is used when ultraviolet (“UV”)curing is the radiation cure technique. In another example, a thermalfree radical initiator is used when thermal or heat curing is theradiation cure technique. It is possible to use a photoinitiator inthermal or heat curing, or a thermal free radical initiator in UVcuring. Thus, the present invention encompasses the use of any initiatorin conjunction with any radiation cure technique so long as theinitiator that is chosen initiates the polymerization process.

[0095] In one embodiment, the free-radical source may alternatively oradditionally be one or more of an electron beam, visible light, UV orgamma radiation, x-rays, or any other high-energy radiation sourcecapable of generating free radicals. Thus in one example, an initiatormay or may not be utilized when gamma radiation, x-ray or electron beamradiation is the radiation cure technique. Such initiators form freeradicals and/or cations that initiate polymerization upon exposure togamma radiation, x-ray or electron beam radiation.

[0096] Optionally, accelerators or catalysts may be included in aprecursor package to control the speed and/or duration of polymerizationand/or crosslinking reaction(s), if a particular component iscrosslinked. Any accelerator or catalyst known to one of ordinary skillin the art or any standard accelerator or catalyst may be used in aprecursor package in the present invention. It should be understood thatthe accelerator or catalyst used in a given precursor package should bechosen based on the specifics of the starting materials, polymerizationscheme, and crosslinking reaction, used to synthesize each polymercomponent or network. In one embodiment, a carboxylic acid compound maybe used as an accelerator, particularly when one of the polymercomponents is a polyurethane.

[0097] Suitable catalysts include, but are not limited to, Lewis acids,for example, such as halides of boron, aluminum, indium, tin, antimony,any transition metal, particularly vanadium, zinc, zirconium, indium,manganese, molybdenum, cobalt, titanium, or tungsten, or mixturesthereof. Exemplary catalysts include chlorides and fluorides of boron,aluminum, or titanium, or mixtures thereof, and more preferably includeboron trifluoride, aluminum trichloride, titanium (III) or (IV)chloride, or mixtures thereof. Other suitable catalysts include, but arenot limited to, Lewis bases, inorganic bases, primary and secondaryamines, and amides. Lewis bases are those compounds containing an atomwith an unshared electron pair in its outer orbital. They are attractedto areas of reduced electron density in the molecules with which theyreact. The organic bases, such as tertiary amines (R₃N:), arerepresentative of the more reactive-type Lewis bases suitable for curingepoxy resins. Other catalysts include, but are not limited to, oxides,such as magnesium oxide, or aluminum oxide; tertiary amines, such asN,N-dimethylaminopyridine, or benzyldimethylamine; imidazoles, such as2-ethyl-4-methylimidazole; and phosphines, such as triphenylphosphine,or tributylphosphine. Catalysts may also include mixtures of any ofthese listed compounds with one or more other components.

[0098] Suitable accelerators include, but are not limited to,sulfonamides, such as benzenesulfonamide; ureas, such as3-(p-chlorophenyl)-1,1-dimethylurea, or3-(3,4-dichlorophenyl)-1,1-dimethylurea; and acids, such as phthalicacid, benzoic acid, or p-toluenesulfonic acid.

[0099] Optionally, additional curing agents may be added to a precursorpackage to facilitate the curing of a polymer component. “Curingagents,” as used herein, means any compound, or combination thereof,capable of connecting at least two polymeric or oligomeric chains,precursors, or macromonomers together under appropriate circumstances.For example, in step-growth or condensation polymers, e.g., such asurethane- or urea-containing systems, a curing agent may serve to buildthe linear molecular weight of a single polymer molecule, to create,e.g., a crosslinked urethane/urea network, or both. As another example,in epoxy-containing systems, a curing agent may simultaneouslyfacilitate polymerization and network formation. In most other types ofpolymers, frequently formed through addition polymerization, curingagents serve only to crosslink polymers that have already been fully ordesirably polymerized.

[0100] Curing agents can be referred to as either “chain extenders,”“crosslinkers,” or both. Suitable chain extenders may vary depending onthe polymers or networks included in the IPN, but, for step-growth orcondensation polymers or epoxies, generally include a polyol, including,for example, telechelic diols, telechelic alkanediols, such as ethyleneglycol, 1,4-butanediol, 1,6-hexanediol, and the like, or mixturesthereof; a polyamine, including, for example, telechelic diamines,telechelic alkanediamines, such as ethylenediamine, propylenediamine,and the like, or mixtures thereof; a cyclic polyol or polyamine, forexample, such as diaminocyclohexane; or mixtures thereof. Suitablecrosslinkers may also vary depending or networks included in the IPN,and include, but are not limited to any chain extender; a disulfide orpolysulfide; a diisocyanate or polyisocyanate; excess diisocyanate orpolyisocyanate; compounds containing or able to generate or activate afree radical; a form of energy able to generate or activate afree-radical, for example, such as heat, visible light, ultravioletlight, x-rays, γ-rays, other energy or radiation, or a mixture thereof;divalent or multivalent salts; or a mixture thereof. In addition, in oneembodiment, the crosslinking of a network, instead of, or in additionto, covalent or ionic crosslinks, may include physical crosslinks, forexample, such as those formed by hydrogen-bonding, provided that the IPNformed has the ability to substantially hold its shape at or around 25°C.

[0101] Other curing agents may be reactive upon addition to a precursorpackage or to a polymer component or may require activation of some sortto begin curing. Certain IPN precursors, prepolymers, or polymers, whenthe proper activators or initiators are used, as understood by those ofordinary skill in the art, can undergo self-polymerization, to formhigher molecular weight polymers, or self-crosslinking, to form anetwork structure, or both. These self-reactions advantageously may befacilitated by one or more catalysts.

[0102] Certain curing agents may already be present in a precursorpackage as they may derive from a functional group or active site on apolymer component. Other curing agents may also be comonomers, forexample, such as multifunctional compounds in step-growth polymerizationreactions, such as polyamines, polyisocyanates, polyols, or the like, ormixtures thereof, or compounds containing two sites across which anaddition polymerization may proceed, such as conjugated dienes,non-conjugated dienes, divinyl compounds, conjugated or non-conjugatedcyclic compounds, divalent or multivalent salts, or mixtures thereof.One of ordinary skill in the art should be able to determine for aparticular IPN system whether certain curing agents function as chainextenders, crosslinkers, or both. It should be understood that anycuring agents already present in a precursor package or useful inanother capacity in the polymer component of the IPN system shall not beconsidered additional curing agents for that polymer component.

[0103] Other compounds useful in polymerization of IPN components alsomay be optionally added to a precursor package as the situationwarrants, which compounds should generally be chosen based on thespecifics of the starting materials, polymerization scheme, andcrosslinking reaction, used to synthesize each polymer component ornetwork. For example, density-modifying fillers, antioxidants,processing aids, processing oils, plasticizers, dyes and pigments, aswell as other additives well known to the skilled artisan may optionallybe added to a precursor package of the present invention in amountssufficient to achieve the purpose for which they are typically used. Italso should be noted that these other compounds should typically notsignificantly degrade or be counterproductive toward polymerization ornetwork formation of other components in the IPNs of the presentinvention.

[0104] IPNs of the present invention contain two or more polymers, atleast one of which is crosslinked to form a network. In consideringpolymers useful in golf balls of the present invention, examples includecrosslinked or uncrosslinked incarnations of any polymer capable ofbeing incorporated into an interpenetrating polymer network.Particularly exemplary polymers include, but are not limited to,polyurea, polyamide/polyurethane copolymer, polyamide/polyureacopolymer, epoxy-end-capped polyurethane, epoxy-end-capped polyurea,polyamide/polyurethane ionomers, polyamide/polyurea ionomers, urethanepolymers or copolymers, polymers made from an epoxy-containingprecursor, polymers having backbone or pendant ester groups, polyimidesor copolymers containing imide groups, polymers or copolymers containingsiloxane groups, polymers or copolymers containing silane groups,acrylate polymers or copolymers (including, but not limited to, mono-,di-, tri, and/or tetra-acrylates), alkyl acrylate polymers orcopolymers, alkyl alkyl-acrylate polymers or copolymers, for example,such as poly(methyl methacrylate) and the like, polyacrylic acids orpoly(alkyl-acrylic acids), including, but not limited to, monomers suchas acrylic acid or methacrylic acid, polymers or copolymers containingvinyl acetate repeat units, polymers or copolymers containing halogengroups, polymers or copolymers containing a uretdione group, polymers orcopolymers containing an oxazolidone group, or mixtures thereof. Otherexamples of useful polymers may include polymers or copolymerscontaining or made from a conjugated diene, polymers or copolymerscontaining a styrenic moiety, ionomeric polymers or copolymers, ormixtures thereof. Preferred first, second or more polymeric componentsinclude monomeric, oligomeric or prepolymeric precursors of vinylresins, polyolefins, polyurethanes, polyureas, polyamide and mixturesand copolymers thereof, such as those described in U.S. Pat. Nos.6,646,061, 6,645,091, 6,648,776, and copending U.S. patent applicationSer. No. 10/190,705, the entirety of which are incorporated herein.

[0105] In one embodiment, an IPN according to the invention may includean acrylate homopolymer or copolymer or a homopolymer or copolymercontaining a conjugated diene, especially polybutadiene, but may notinclude both.

[0106] When a urethane polymer and a polymer made from anepoxy-containing precursor are both present in an IPN of the presentinvention, it is preferable that at least about 50% by weight of the IPNinclude the urethane polymer network, more preferably at least about80%, most preferably at least about 90%, for golf ball applications.

[0107] Interpenetrating polymer networks according to the presentinvention may typically be fabricated by a number of different methodsknown to one of ordinary skill in the art. Such fabrication processesinclude, but are not limited to, the following groups of methods.

[0108] (1) At least two sets of pre-synthesized oligomeric or polymericcomponents are mixed together by any standard method or any method knownto one of ordinary skill in the art, such as, for example, melt mixing,solvating at least one component in a solution of at least one of theother components and a solvent or solvent mixture, or forming a solutionmixture from at least two solutions, each containing at least one set ofcomponents and a solvent or solvent mixture. In cases where solventmixing is involved, the majority of the solvent or solvent mixtureshould be removed after mixing, for example, by evaporation, boiling,precipitation of the non-solvent components, or the like, preferablysuch that the IPN contains less than 10% solvent, or more preferably issubstantially free of solvent. The mixing process should allow forsufficiently intimate mixing of the components, for example, such thatthe at least two components are at least partially co-entangled. Atleast one of the at least two intimately mixed components can then becrosslinked. If both components are to be crosslinked, the crosslinkingcan occur simultaneously or sequentially.

[0109] (2) At least one non-polymerized precursor package can beincorporated into at least one other pre-synthesized oligomeric orpolymeric component, which may or may not already be a crosslinkednetwork, which incorporation can occur by any method that facilitatesintimate mixing of the at least one precursor package with the at leastone pre-synthesized component, for example, such as by swelling the atleast one pre-synthesized component with the at least one precursorpackage, optionally under an applied pressure. Once the components areintimately mixed, the at least one precursor package can then beappropriately polymerized. In the event that the at least onepre-synthesized component is/are already crosslinked and a semi-IPN isdesired, a further crosslinking reaction may not be necessary.Otherwise, at least one component of the at least one precursor package,now polymerized, may be crosslinked. Alternately, at least one componentof the at least one precursor package may be crosslinked and polymerizedsimultaneously. If the at least one pre-synthesized component is/are notalready crosslinked, then the at least one pre-synthesized component andthe at least one polymerized precursor package component may becrosslinked simultaneously or sequentially. Alternately, if the at leastone pre-synthesized component is/are not already crosslinked and asemi-IPN is desired, at least one of either set of components can becrosslinked.

[0110] (3) The at least two precursor packages can be mixed together byany method that facilitates intimate mixing of the compounds in the atleast two precursor packages. The at least two intimately mixedprecursor packages can then be polymerized and/or crosslinked in anyorder to form an IPN of the present invention. In one embodiment, the atleast two precursor packages can be polymerized simultaneously orsequentially, but not crosslinked, yielding an intimately mixed blend ofthe at least two polymerized precursor package components. Then, one ormore of the polymerized components can be crosslinked by an appropriatecrosslinking method, and, if more than one of the polymerized componentsare to be crosslinked, the crosslinking can be done simultaneously orsequentially. Alternately, for one or more of the polymerizedcomponents, the crosslinking reaction may occur simultaneously with thepolymerization reaction. In another embodiment, at least one of the atleast two intimately mixed precursor packages can be polymerized andcrosslinked in the presence of the other precursor package(s), afterwhich the subsequent steps are similar to method #2 (after the initialintimate mixing).

[0111] It should be understood that certain rapid-forming IPN systemsmay need to be prepared using a quick-forming process, such as reactioninjection molding (RIM), which is a processing method known for use informing articles or materials out of rapidly curing polymer systems.Thus, the faster the formation of a given IPN system, the more suitablethe use of RIM to process it. Indeed, if the IPN gelation time is lessthan about 60 seconds, preferably less than about 30 seconds, RIM ispreferred over other conventional processing techniques. In the RIMprocess, at least two or more reactive, low-viscosity, liquid componentsare generally mixed, for example, by impingement, and injected underhigh pressure (e.g., at or above about 1200 psi) into a mold. Thereaction times for RIM system's are much faster than in conventionallower-pressure mixing and metering equipment. The precursor packagesused for the RIM process, therefore, are typically much lower inviscosity to better facilitate intimate mixing in a very short time.

[0112] (4) Each of the at least two precursor packages can be at leastpartially polymerized separately, and preferably simultaneously, atwhich point the at least partially polymerized precursor packages can bemixed together in a manner sufficient to result in intimate mixing ofthe components of the at least two, at-least-partially-polymerizedcomponents. In some urethane-epoxy systems, the total gelation time mayrange from about 40 to 100 seconds. The remainder of the polymerizationsof the intimately mixed components then occur simultaneously, althoughone polymerization may be sufficiently complete before any other. Then,after all polymerizations are sufficiently complete, one or more of thepolymerized components can be crosslinked by an appropriate crosslinkingmethod, and, if more than one of the polymerized components are to becrosslinked, the crosslinking can be done simultaneously orsequentially. Alternately, for one or more of the polymerizedcomponents, the crosslinking reaction may occur simultaneously with thepolymerization reaction.

[0113] Crosslinking agents for each of the components, if necessary, maybe mixed in with the pre-synthesized components initially, especially ifthey need to be externally activated, or may be added subsequent to theintimate mixing step, especially to avoid premature crosslinking byheating or exposure to activating energy or compounds. If activation isneeded for crosslinking one or more of the at least two intimately mixedcomponents, it is typically performed after an intimate mixing step.Activators for crosslinking may affect an agent or a part of thecomponent itself, for example, such as a carbon-carbon double bond or alabile carbon-hydrogen bond, and generally include, but are not limitedto, heat, light, UV radiation, x-rays, microwave radiation, and gammaradiation.

[0114] It should be understood that each method of crosslinking shouldbe chosen to match up with the choice of starting materials andpolymerization scheme used to synthesize each polymer component. Itshould also be noted that each method of crosslinking should typicallynot significantly degrade or be counterproductive toward polymerizationor network formation of other components in the IPNs of the presentinvention.

[0115] The formation of an IPN, in accordance of the present invention,may involve one or more polymerization and/or crosslinking techniques topolymerize or crosslink the polymer systems of the IPN. As used herein,the phrase “polymerization and/or crosslinking techniques” refers to theoptional use of one or more initiators in conjunction with the chosenradiation cure technique or techniques. Thus in one embodiment, theformation of an IPN of the present invention comprises polymerizingand/or crosslinking one or more polymers, prepolymers, oligomers and/ormonomers sequentially or simultaneously using one or more polymerizationand/or crosslinking techniques. In particular, the formation of an IPNcomprises sequentially or simultaneously exposing one or more polymers,prepolymers, oligomers and/or monomers to: 1) an energy source selectedfrom the group consisting of thermal/heat (i.e., microwave or infrared),UV radiation, visible radiation, electron beam radiation, x-rayradiation, gamma radiation, and combinations thereof, in the presence ofan initiator; and 2) optionally one or more additional energy sourcesselected from the group consisting of thermal/heat (i.e., microwave orinfrared), UV radiation, visible radiation, electron beam radiation,x-ray radiation, gamma radiation, and combinations thereof, in thepresence of an initiator. As discussed above, the initiator is optionaland can be present or absent when electron beam radiation, x-rayradiation, thermal radiation, or gamma radiation is utilized in formingan IPN.

[0116] The energy source is selected such that its exposure to one ormore polymers, prepolymers, oligomers and/or monomers does not adverselyor detrimentally affect crosslinking and/or polymerization reactions orthe characteristics of the final crosslinked and/or polymerized IPN. Inone example, an IPN comprising polyurea and acrylate requires lowtemperature for a fast cure of polyurea prepolymer, but curing theacrylate system generally requires heat, which adversely affects thecuring of the polyurea by reducing the reaction rate and cosmeticallychanging cured polyurea. Electron beam radiation may be chosen to curethe acrylate because it can be utilized while avoiding the adverse ordetrimental effects caused heat.

[0117] In preferred embodiment, the one or more additional energy sourceis electron beam radiation. In particular, the formation of an IPNcomprises sequentially or simultaneously exposing one or more polymers,prepolymers, oligomers and/or monomers to: 1) an energy source selectedfrom the group consisting of thermal radiation/heat, UV radiation,visible radiation, electron beam radiation, x-ray radiation, gammaradiation, and combinations thereof; and 2) electron beam radiation. Theuse of a low power electron beam source allows more efficient dosage ofelectrons and also helps prevent unwanted reactions with the finalcrosslinked/polymerized IPN.

[0118] The electron beam tube is a vacuum tube having a base end and awindow end. An extended filament is disposed within the beam tubeproximate to the base end. The filament generates electrons inconjunction with electron beam forming electrodes. The electrons fromthe filament (i.e., electron beam source) are directed toward andthrough the beam window of the electron beam tube. A low power electronbeam tube is preferred. The beam energy from a low power beam tube isbelow about 125 kV (kilovolts), typically between about 15-80 kV (or anyvalue therebetween), more typically between about 20-75 kV and mosttypically between about 30-65 kV. The voltage to the power supply (inputvoltage from about 10 to about 1,000 volts) is preferably about 110volts (or less) and its operating power is preferably about 100 watts(or less). However, the output voltage of the beam tube may be between20-100 kV or any value therebetween. Likewise, the operating power ofthe electron beam may be from about 10-1,000 watts or any valuetherebetween.

[0119] In one preferred embodiment, the precursor packages are mixedseparately until a sufficient viscosity is attained, preferably fromabout 2,000 cPs to 35,000 cPs, more preferably from about 8,000 cPs to30,000 cPs, most preferably from about 15,000 cPs to 26,000 cPs.

[0120] The golf balls of the present invention can likewise include oneor more homopolymeric or copolymeric thermoplastic or thermosetmaterials in a center, an intermediate layer, and/or a cover, eitherindividually or in combination with any other available materials or ina blend with any IPN according to the invention. In one embodiment, theone or more portions of the ball including IPN material will not includeblends with conventional materials. One of ordinary skill in the artwould know that most of the polymeric materials listed below may belongin the thermoplastic category or in the thermoset category, dependingupon the nature of the repeat units, functional groups pendant from therepeat units, method of polymerization, method of formation, temperatureof formation, post-polymerization treatments, and/or many other possiblefactors, and are suitable for use in golf balls according to theinvention. The materials include, but are not limited to, the followingpolymers, or their set of monomeric, oligomeric, or macromonomericprecursors:

[0121] (1) Vinyl resins, for example, such as those formed by thepolymerization of vinyl chloride, or by the copolymerization of vinylchloride with vinyl acetate, acrylic esters or vinylidene chloride;

[0122] (2) Polyolefins, for example, such as polyethylene,polypropylene, polybutylene, and copolymers, such as ethylenemethylacrylate, ethylene ethylacrylate, ethylene vinyl acetate, ethylenemethacrylic acid, ethylene acrylic acid, or propylene acrylic acid, aswell as copolymers and homopolymers, such as those produced using asingle-site catalyst or a metallocene catalyst;

[0123] (3) Polyurethanes, for example, such as those prepared fromdiols, triols, or polyols and diisocyanates, triisocyanates, orpolyisocyanates, as well as those disclosed in U.S. Pat. No. 5,334,673;

[0124] (4) Polyureas, for example, such as those prepared from diamines,triamines, or polyamines and diisocyanates, triisocyanates, orpolyisocyanates, as well as those disclosed in U.S. Pat. No. 5,484,870;

[0125] (5) Polyamides, for example, such as poly(hexamethyleneadipamide) and others prepared from diamines and dibasic acids, as wellas those from amino acids such as poly(caprolactam), and blends ofpolyamides with SURLYN, polyethylene, ethylene copolymers,ethyl-propylene-non-conjugated diene terpolymer, and the like;

[0126] (6) Acrylic resins and blends of these resins with, for example,polymers such as poly vinyl chloride, elastomers, and the like;

[0127] (7) Olefinic rubbers, for example, such as blends of polyolefinswith ethylene-propylene-non-conjugated diene terpolymer; blockcopolymers of styrene and butadiene, isoprene or ethylene-butylenerubber; or copoly(ether-amide), such as PEBAX, sold by ELF Atochem ofPhiladelphia, Pa.;

[0128] (8) Polyphenylene oxide resins or blends of polyphenylene oxidewith high impact polystyrene, for example, as sold under the trademarkNORYL by General Electric Company of Pittsfield, Mass.;

[0129] (9) Polyesters, for example, such as polyethylene terephthalate,polybutylene terephthalate, polyethylene terephthalate/glycol modifiedand elastomers, such as sold under the trademarks HYTREL by E.I. DuPontde Nemours & Co. of Wilmington, Del., and LOMOD by General ElectricCompany of Pittsfield, Mass.;

[0130] (10) Blends and alloys, for example including polycarbonate withacrylonitrile butadiene styrene, polybutylene terephthalate,polyethylene terephthalate, styrene maleic anhydride, polyethylene,elastomers, and the like, and polyvinyl chloride with acrylonitrilebutadiene styrene, ethylene vinyl acetate, or other elastomers;

[0131] (11) Blends of vulcanized, unvulcanized, or non-vulcanizablerubbers with polyethylene, propylene, polyacetal, nylon, polyesters,cellulose esters, and the like; and

[0132] (12) Polymers or copolymers possessing epoxy-containing, orpost-polymerization epoxy-functionalized, repeat units, for example, incombination with anhydride, ester, amide, amine, imide, carbonate,ether, urethane, urea, .alpha.-olefin, conjugated, or acid (optionallytotally or partially neutralized with inorganic salts) comonomers, orcopolymers or blends thereof.

[0133] The wound layer, if present, is typically disposed about the coreand includes a tensioned thread material. Many different kinds of threadmaterials may be used for the wound layer of the present invention. Thethread may be single-ply or may include two or more plies. Preferably,the thread of the present invention is single-ply. The thread may beselected to have different material properties, dimensions,cross-sectional shapes, and methods of manufacturing. If two or morethreads are used, they may be identical in material and mechanicalproperties or they may be substantially different from each other,either in cross-section shape or size, composition, elongated state, andmechanical or thermal properties. Mechanical properties that may bevaried include resiliency, elastic modulus, and density. Thermalproperties that may be varied include melt temperature, glass transitiontemperature and thermal expansion coefficient.

[0134] The tensioned thread material of the wound layer may encompassany suitable material, but typically includes fiber, glass, carbon,polyether urea, polyether block copolymers, polyester urea, polyesterblock copolymers, syndiotactic- or isotactic-poly(propylene),polyethylene, polyamide, poly(oxymethylene), polyketone, poly(ethyleneterephthalate), poly(p-phenylene terephthalamide), poly(acrylonitrile),diaminodicyclohexylmethane, dodecanedicarboxylic acid, natural rubber,polyisoprene rubber, styrene-butadiene copolymers,styrene-propylene-diene copolymers, another synthetic rubber, or block,graft, random, alternating, brush, multi-arm star, branched, ordendritic copolymers, or mixtures thereof.

[0135] Threads used in the present invention may be formed using avariety of processes including conventional calendering and slitting,melt spinning, wet spinning, dry spinning and polymerization spinning.Any process available to one of ordinary skill in the art may beemployed to produce thread materials for use in the wound layer. Thetension used in winding the thread material of the wound layer may beselected as desired to provide beneficial playing characteristics to thefinal golf ball. The winding tension and elongation may be kept the sameor may be varied throughout the layer. Preferably, the winding occurs ata consistent level of tension so that the wound layer has consistenttension throughout the layer.

[0136] In addition, the winding patterns used for the wound layer can bevaried in any way available to those of ordinary skill in the art.Although one or more threads may be combined to begin forming the woundlayer, it is preferred to use only a single continuous thread.

[0137] The cover provides the interface between the ball and a club.Properties that are desirable for the cover include good moldability,high abrasion resistance, high tear strength, high resilience, and goodmold release, among others. The cover typically provides goodperformance characteristics and durability.

[0138] A free-radical source, often alternatively referred to as afree-radical initiator, may optionally be used in one or more layers ofthe golf balls according to the invention, particularly when a polymercomponent includes a thermoset material. The free-radical source fornon-IPN components may be similar to that used in an IPN of the presentinvention or may be selected from the same or other suitable compounds.

[0139] The free radical source for non-IPN components is preferably aperoxide, more preferably an organic peroxide. The peroxide is typicallypresent in an amount greater than about 0.1 parts per hundred of thetotal polymer component, preferably about 0.1 to 15 parts per hundred ofthe polymer component, and more preferably about 0.2 to 5 parts perhundred of the total polymer component. It should be understood by thoseof ordinary skill in the art that the presence of certain components mayrequire a larger amount of free-radical source than the amountsdescribed herein. The free radical source may alternatively oradditionally be one or more of an electron beam, UV or gamma radiation,x-rays, or any other high energy radiation source capable of generatingfree radicals. It should be further understood that heat oftenfacilitates initiation of the generation of free radicals when peroxidesare used as a free-radical initiator.

[0140] Fillers added to one or more layers of the golf ball typicallyinclude processing aids or compounds to affect rheological and mixingproperties, the specific gravity (i.e., density-modifying fillers), themodulus, the tear strength, reinforcement, and the like. A densityadjusting filler may be used to control the moment of inertia, and thusthe initial spin rate of the ball and spin decay. Fillers are typicallypolymeric or inorganic in nature, and, when used, are typically presentin an amount from about 0.1 to 50 weight percent of the layer in whichthey are included. Any suitable filler available to one of ordinaryskill in the art may be used. Exemplary fillers include, but are notlimited to, precipitated hydrated silica; clay; talc; glass fibers;aramid fibers; mica; calcium metasilicate; barium sulfate; zinc sulfide;lithopone; silicates; silicon carbide; diatomaceous earth; polyvinylchloride; carbonates such as calcium carbonate and magnesium carbonate;metals such as titanium, tungsten, aluminum, bismuth, nickel,molybdenum, iron, copper, boron, cobalt, beryllium, zinc, and tin; metalalloys such as steel, brass, bronze, boron carbide whiskers, andtungsten carbide whiskers; metal oxides such as zinc oxide, iron oxide,aluminum oxide, titanium oxide, magnesium oxide, and zirconium oxide;particulate carbonaceous materials such as graphite, carbon black,cotton flock, natural bitumen, cellulose flock, and leather fiber; microballoons such as glass and ceramic; fly ash; cured, ground rubber; orcombinations thereof.

[0141] Fillers may also include various foaming agents or blowing agentswhich may be readily selected by one of ordinary skill in the art.Foamed polymer blends may be formed by blending ceramic or glassmicrospheres with polymer material. Polymeric, ceramic, metal, and glassmicrospheres may be solid or hollow, and filled or unfilled. Fillers aretypically also added to one or more portions of the golf ball to modifythe density thereof to conform to uniform golf ball standards. Fillersmay also be used to modify the weight of the center or at least oneadditional layer for specialty balls, e.g., a lower weight ball ispreferred for a player having a low swing speed.

[0142] Additional materials conventionally included in golf ballcompositions also may be present. These additional materials include,but are not limited to, density-adjusting fillers, coloring agents,reaction enhancers, whitening agents, UV absorbers, hindered amine lightstabilizers, defoaming agents, processing aids, and other conventionaladditives. Stabilizers, softening agents, plasticizers, includinginternal and external plasticizers, impact modifiers, foaming agents,excipients, reinforcing materials and compatibilizers can also be addedto any composition of the invention. All of these materials, which arewell known in the art, are added for their usual purpose in typicalamounts.

[0143] Methods for measuring the resiliency of golf balls are well knownby those of ordinary skill in the art. One method of measuring theresiliency of a ball at impact is to utilize an air cannon or othermeans of propelling a ball at velocities equivalent to those of a golfclub head. The balls are fired at a massive rigid block, with theinbound and outbound velocities being measured. The velocity may bemeasured by the use of light screens, which measure the time requiredfor the ball to travel a fixed distance. The fixed distance divided bythe transit time is equivalent to the average velocity of the ball overthe fixed distance. The ratio of the outbound velocity to the inboundvelocity is commonly referred to as the coefficient of restitution(“COR”). The COR is a direct measure of the resilience of a golf ball ata particular inbound velocity. Since golf balls behave in a relativelylinear viscoelastic fashion, inbound ball velocity is typicallyfunctionally equivalent to club swing speed, which is set in thestandardized COR test at about 125 ft/sec.

[0144] The use of various dimple patterns and profiles provides arelatively effective way to modify the aerodynamic characteristics of agolf ball. As such, the manner in which the dimples are arranged on thesurface of the ball can be by any available method. For instance, theball may have an icosahedron-based pattern, such as described in U.S.Pat. No. 4,560,168, or an octahedral-based dimple patterns as describedin U.S. Pat. No. 4,960,281. The resultant golf balls prepared accordingto the invention typically will have dimple coverage greater than about60 percent, preferably greater than about 65 percent, and morepreferably greater than about 70 percent.

[0145] The golf balls typically have a coefficient of restitution ofgreater than about 0.7, preferably greater than about 0.75, and morepreferably greater than about 0.78. Alternatively, the maximum COR ofthe ball is one that does not cause the golf ball to exceed initialvelocity requirements established by regulating entities such as theUSPGA. As used herein, the term “coefficient of restitution” (CoR) iscalculated by dividing the rebound velocity of the golf ball by theincoming velocity when a golf ball is shot out of an air cannon. The CoRtesting is conducted over a range of incoming velocities and determinedat an inbound velocity of 125 ft/s. Another measure of this resilienceis the “loss tangent,” or tan *, which is obtained when measuring thedynamic stiffness of an object. Loss tangent and terminology relating tosuch dynamic properties is typically described according to ASTMD4092-90. Thus, a lower loss tangent indicates a higher resiliency,thereby indicating a higher rebound capacity. Low loss tangent indicatesthat most of the energy imparted to a golf ball from the club isconverted to dynamic energy, i.e., launch velocity and resulting longerdistance. The rigidity or compressive stiffness of a golf ball may bemeasured, for example, by the dynamic stiffness. A higher dynamicstiffness indicates a higher compressive stiffness. To produce golfballs having a desirable compressive stiffness, the dynamic stiffness ofthe crosslinked material should be less than about 50,000 N/m at −50° C.Preferably, the dynamic stiffness should be between about 10,000 and40,000 N/m at −50° C., more preferably, the dynamic stiffness should bebetween about 20,000 and 30,000 N/m at −50° C.

[0146] The golf balls also typically have a compression of no greaterthan about 120. In one preferred embodiment, the compression is at leastabout 40. In another preferred embodiment, the compression is from about50 to 120, preferably from about 60 to 100. As used herein, the term“compression” refers to “Atti compression” and is defined as thedeflection of an object or material relative to the deflection of acalibrated spring, as measured with an Atti Compression Gauge, that iscommercially available from Atti Engineering Corp. of Union City, N.J.Atti compression is typically used to measure the compression of a golfball and/or a golf ball core. Compression values are dependent on thediameter of the article being measured.

[0147] The golf ball layers containing the IPNs according to the presentinvention typically have a material hardness greater than about 15 ShoreA, preferably from about 15 Shore A to 85 Shore D. In one preferredembodiment, the material hardness is from about 10 to 85 Shore D. Itshould be understood, especially to one of ordinary skill in the art,that there is a fundamental difference between “material hardness” and“hardness, as measured directly on a golf ball.” Material hardness isdefined by the procedure set forth in ASTM-D2240-00 and generallyinvolves measuring the hardness of a flat “slab” or “button” formed ofthe material of which the hardness is to be measured. Generally,ASTM-D2240-00 requires calibration of durometers, which have scalereadings from 0 to 100. However, readings below 10 or above 90 are notconsidered reliable, as noted in ASTM-D2240-00, and accordingly, all thehardness values herein are within this range.

[0148] Additionally, the butadiene rubber that may be used in one ormore layers of the golf balls prepared according to the presentinvention, in an uncured state, typically has a Mooney viscosity greaterthan about 20, preferably greater than about 30, and more preferablygreater than about 40. Mooney viscosity is typically measured accordingto ASTM D1646-99.

[0149] Dimensions of golf ball components, i.e., thickness and diameter,may vary depending on the desired properties. For the purposes of theinvention, any layer thickness may be employed. Non-limiting examples ofthe various embodiments outlined above are provided here with respect tolayer dimensions.

[0150] The present invention relates to golf balls of any size, althoughthe golf ball preferably meets USGA standards of size and weight. While“The Rules of Golf” by the USGA dictate specifications that limit thesize of a competition golf ball to more than 1.680 inches in diameter,golf balls of any size can be used for leisure golf play. The preferreddiameter of the golf balls is from about 1.680 inches to about 1.800inches. The more preferred diameter is from about 1.680 inches to about1.760 inches. A diameter of from about 1.680 inches (43 mm) to about1.740 inches (44 mm) is most preferred, however diameters anywhere inthe range of from 1.700 to about 1.950 inches can be used. Preferably,the overall diameter of the core and all intermediate layers is about 80percent to about 98 percent of the overall diameter of the finishedball.

[0151] A spin rate of a golf ball refers to the speed it spins on anaxis while in flight, measured in revolutions per minute (“rpm”). Spingenerates lift, and accordingly, spin rate directly influences how highthe ball flies and how quickly it stops after landing. The golf ballsdisclosed herein can be tested to determine spin rate by initiallyestablishing test conditions using suitable control golf balls and golfclubs. For example, a spin rate of a golf ball struck by a standard golfdriver was obtained by using test conditions for a Titleist PinnacleGold golf ball that gives a ball speed of about 159 to about 161miles/hour, a launch angle of about 9.0 degrees to about 10.0 degrees,and a spin rate of about 2900 rpm to about 3100 rpm. Thus in oneembodiment, the spin rate of a golf ball hit with a golf club driverunder the same test conditions is between about 1200 rpm to about 4000rpm. In a preferred embodiment, the spin rate of a golf ball hit with agolf club driver is between about 2000 rpm to about 3500 rpm, morepreferably between about 2500 and 3000 rpm.

[0152] For an 8-iron ball spin test, a spin rate of a golf ball struckby a standard 8-iron club was obtained by using test conditions for aTitleist Pro V1 golf ball that gives a ball speed of about 114 to about116 miles/hour, a launch angle of about 18.5 to about 19.5 degrees and aspin rate of about 8100 rpm to about 8300 rpm. Thus in one embodiment,the spin rate of an average, cleanly struck 8-iron shot is between 6500rpm and 10,000 rpm. In preferred embodiment, the spin rate of anaverage, cleanly struck 8-iron shot under the same test conditions isbetween 7500 rpm and 9500 rpm, more preferably between about 8000 rpmand 9000 rpm.

[0153] Referring to FIG. 1, a golf ball 10 of the present invention caninclude a center 12 and a cover 16 surrounding the center 12. Referringto FIG. 2, a golf ball 20 of the present invention can include a center22, a cover 26, and at least one intermediate layer 24 disposed betweenthe cover and the center. In one embodiment, the intermediate layer 24is disposed within the core, which also includes a center 22 and mayoptionally include a wound layer (not shown). In another embodiment, theintermediate layer 24 is disposed outside of the core, which mayoptionally include a wound layer (not shown), but which is disposedunder the cover layer 26. Each of the cover and center layers in FIG. 1or 2 may include more than one layer; i.e., the golf ball can be aconventional three-piece wound ball, a two-piece ball, a ball having amulti-layer core and an intermediate layer or layers, etc. Also, FIG. 3shows a golf ball 30 of the present invention including a center 32, acover 38, and an intermediate layer 34 located within the core 33.Alternately, also referring to FIG. 3, a golf ball 30 of the presentinvention can include a center 32, a cover 38, and an intermediate layer36 disposed between the cover and the core 33. Although FIG. 3 showsgolf balls with only one intermediate layer, it will be appreciated thatany number or type of intermediate layers may be used whether inside oroutside the core, or both, as desired. Further, any of the FIGS.detailed herein may include embodiments wherein an optional wound layeris disposed between the center and the core of the golf ball.

[0154] In the golf balls of any of the aforementioned FIGS., the layercontaining the IPN material may be outside the core or the center, inone embodiment. In another embodiment, the layer containing the IPNmaterial may be inside the cover layer. In yet another embodiment, thelayer containing the IPN material may be in any layer of the golf ball.

[0155] Although the disclosure herein focuses on a method of making anIPN layer for golf balls, it is also easily applicable by one ofordinary skill in the art to the manufacture of other items, such ascuring adhesives (e.g., in golf shoes), IPN coatings with crosslinkablesystems, and in any application that requires post-crosslinking of thepolymer.

EXAMPLES

[0156] The following examples are only representative of the methods andmaterials for use in golf ball compositions and golf balls of thisinvention, and are not to be construed as limiting the scope of theinvention in any way.

Example 1 Golf Ball Having a Urethane-Epoxy IPN Present in the CoverLayer

[0157] The golf ball of Example 1 was prepared with a 1.585 inch (about4.03 cm) wound core around a fluid-filled center. The golf ball had afinished diameter of about 1.68 inches (about 4.27 cm). The golf ball ofExample 1 included an IPN of a polyurethane and an epoxy polymer,wherein the epoxy polymer component was about 5% of the IPN and thepolyurethane component was about 95% of the IPN. The urethane precursorpackage in Example 1 included Vibrathane B-821 prepolymer,1,4-butanediol, and T-12 dibutyltin dilaurate catalyst. The molarproportion of isocyanate groups in the Vibrathane prepolymer to hydroxylgroups in the diol was in about a 1:0.95 ratio. The epoxy precursorpackage included an epoxy resin (DER 331) and a BF₃ catalyst/curingagent to facilitate self-polymerization and self-crosslinking to form anepoxy network. In order to limit the possibility of the polyurethanebeing further chain extended with the curing agent intended for curingthe epoxy component, the epoxy curing agent was chosen to be catalyticand substantially unreactive with the polyurethane component. The epoxycuring agent chosen to prepare the ball of Example 1 was aBF₃:4-chlorobenzenamine catalyst complex. Other epoxy curing agentsinclude, but are not limited to, oxides, such as magnesium oxide, oraluminum oxide; tertiary amines, such as N,N-dimethylaminopyridine, orbenzyldimethylamine; imidazoles, such as 2-ethyl-4-methylimidazole; andphosphines, such as triphenylphosphine, or tributylphosphine.

[0158] The respective precursor packages were mixed separately until asufficient viscosity was achieved to allow mixing by hand, or from about8,000 cPs to 35,000 cPs, after which the precursor packages were mixedtogether and cast as the cover layer on wound cores to form the golfball of Example 1. The total gelation time was about 80 seconds. TABLE 1Cover/Ball Characteristics Control Example 1 Urethane component BDVibrathane/BD Vibrathane/BD precursor package (1:0.95) + 0.01%(1:0.95) + 0.01% T-12 catalyst T-12 catalyst (95%) Epoxy componentprecursor — DER 331/10 pph package BF₃ catalyst (5%) Coefficient ofRestitution 0.81 0.81 Corrected Compression 87 90 Material Hardness 3831 (Shore D) Cover Hardness (Shore D) 46 43 Initial Velocity (ft/sec)255.5 255 T_(g) peak (° C., measured by −71 −67 DSC) T_(g) width (° C.,measured by 17 24 DSC) # commercially from BASF of Parsippany, NJ; T-12represents a dibutyl tin dilaurate catalyst, which is availablecommercially from Air Products of Allentown, PA; DER # 331 represents anepoxy resin based on a diglycidyl ether of bisphenol A (DGEBA) and iscommercially available from Dow Chemical # Company of Midland, MI; BF₃catalyst represents a trifluoroboron-4-chlorobenzenamine catalystcomplex and is commercially available from Air Products of Allentown,PA.

Example 2 Golf Ball Having a Urethane-Polybutadiene Diacrylate IPNPresent in the Cover Layer

[0159] The golf ball of Example 2 includes an IPN of a polyurethane anda polybutadiene copolymer, which is prepared with a 1.585 inch (about4.03 cm) wound core around a fluid-filled center. Note that the IPN'sdisclosed in the Examples and specification herein can be used in anygolf ball construction. The golf ball has a finished diameter of about1.68 inches (about 4.27 cm). The golf ball of Example 2 includes an IPNof a polyurethane and a polybutadiene diacrylate copolymer, wherein thepolybutadiene copolymer component is about 10% of the IPN and thepolyurethane component is about 90% of the IPN. The urethane precursorpackage in Example 2 includes Vibrathane B-821 prepolymer,1,4-butanediol, and T-12 dibutyltin dilaurate catalyst. The molarproportion of isocyanate groups in the Vibrathane prepolymer to hydroxylgroups in the diol is in about a 1:0.95 ratio. The polybutadienediacrylate copolymer precursor package includes butadiene monomer or apolybutadiene resin, a diacrylate crosslinking agent, and an initiatorto facilitate crosslinking to form a polybutadiene diacrylate network.In order to limit the possibility of degradation of, or interferencewith, the polyurethane chain extension reaction, the polybutadienediacrylate copolymer crosslinking initiator preferably is chosen to besubstantially unreactive with the polyurethane. The initiator chosen toprepare the ball of Example 2 is a peroxide initiator, particularlydibenzoyl peroxide.

[0160] The respective precursor packages are mixed separately until asufficient viscosity is achieved to allow mixing by hand, or from about8,000 cPs to 35,000 cPs, after which the precursor packages are mixedtogether and cast as the cover layer on wound cores to form the golfball of Example 2.

Example 3 Golf Ball Having a Urethane-Acrylate IPN Present in the CoverLayer

[0161] The golf ball of Example 3 is prepared with a 1.585 inch (about4.03 cm) wound core around a fluid-filled center. Again, note that theIPN's disclosed in the Examples and specification herein can be used inany golf ball construction. The golf ball has a finished diameter ofabout 1.68 inches (about 4.27 cm). The golf ball of Example 3 includesan IPN of a polyurethane and an acrylate polymer, wherein the acrylatepolymer component is about 10% of the IPN and the polyurethane componentis about 90% of the IPN. The urethane precursor package in Example 3includes Vibrathane B-821 prepolymer, 1,4-butanediol, and T-12dibutyltin dilaurate catalyst. The molar proportion of isocyanate groupsin the Vibrathane prepolymer to hydroxyl groups in the diol is in abouta 1:0.95 ratio. The acrylate precursor package includes methylmethacrylate monomer, optionally a crosslinking agent (such as adiacrylate), and an initiator to facilitate polymerization (andoptionally crosslinking) to form a methyl methacrylate polymer (andoptionally network). In order to limit the possibility of degradationof, or interference with, the polyurethane chain extension reaction, themethyl methacrylate polymerization initiator is chosen to preferably besubstantially unreactive with the polyurethane. The initiator chosen toprepare the ball of Example 3 is a free radical initiator, such asazobisisobutyronitrile (AIBN).

[0162] The respective precursor packages are mixed separately until asufficient viscosity is achieved to allow mixing by hand, or from about8,000 cPs to 35,000 cPs, after which the precursor packages are mixedtogether and cast as the cover layer on wound cores to form the golfball of Example 3.

Example 4 Golf Ball Having a Urethane-Epoxy IPN Present in the CoverLayer

[0163] The golf ball of Example 4 is prepared with a 1.585 inch (about4.03 cm) wound core around a fluid-filled center. Yet again, note thatthe IPN's disclosed in the Examples and specification herein can be usedin any golf ball construction. The golf ball has a finished diameter ofabout 1.68 inches (about 4.27 cm). The golf ball of Example 4 includesan IPN of a polyurethane and an epoxy polymer, wherein the epoxy polymercomponent is about 10% of the IPN and the polyurethane component isabout 90% of the IPN. The urethane precursor package in Example 4includes Vibrathane B-821 prepolymer, 1,4-butanediol, and optionally acatalyst, such as T-12 dibutyltin dilaurate. The molar proportion ofisocyanate groups in the Vibrathane prepolymer to hydroxyl groups in thediol is in about a 1:0.95 ratio. The epoxy precursor package includes anepoxy resin (DER 331), a BF₃ catalyst/curing agent to facilitateself-polymerization and self-crosslinking to form an epoxy network, anda catalyst to facilitate occasional interreactions of the urethane andthe epoxy precursors or networks in the form of oxazolidone functionalgroups. In order to limit the possibility of the polyurethane beingfurther chain extended with the curing agent intended for curing theepoxy component, the epoxy curing agent is chosen to preferably becatalytic and substantially unreactive with the polyurethane component.The epoxy curing agent chosen to prepare the ball of Example 4 is aBF₃:4-chlorobenzenamine catalyst complex. The oxazolidone formationcatalyst chosen to prepare the ball of Example 4 is ethylmethylimidazole.

[0164] The respective precursor packages are mixed separately until asufficient viscosity is achieved to allow mixing by hand, or from about8,000 cPs to 35,000 cPs, after which the precursor packages are mixedtogether and cast as the cover layer on wound cores to form the golfball of Example 4.

[0165] It is to be understood that the invention is not to be limited tothe exact configuration as illustrated and described herein. Forexample, it should be apparent that a variety of materials would besuitable for use in the composition or method of making the golf ballsaccording to the Detailed Description of the Preferred Embodiments.Accordingly, all expedient modifications readily attainable by one ofordinary skill in the art from the disclosure set forth herein, or byroutine experimentation therefrom, are deemed to be within the spiritand scope of the invention as defined by the appended claims.

[0166] The invention described and claimed herein is not to be limitedin scope by the specific embodiments herein disclosed, since theseembodiments are intended as illustrations of several aspects of theinvention. Any equivalent embodiments are intended to be within thescope of this invention. Indeed, various modifications of the inventionin addition to those shown and described herein will become apparent tothose skilled in the art from the foregoing description. For example,the compositions of the present invention may be used in a variety ofgolf equipment, for example, golf shoes for sole applications, as wellas in inserts for golf putters. Such modifications are also intended tofall within the scope of the appended claims.

Example 5 Electron Beam Cure of Polyurea Prepolymer/Urea Acrylate

[0167] Various mixtures containing polyurea prepolymer/curative and ureaacrylate were cured using either electron beam radiation or thermalradiation and the DMA of resulting interpenetrating polymer networkswere analyzed and compared with respect to their crosslink density. Thecurative in the polyurea prepolymer/curative mixture is CLEARLINK 1000,which can have a polyurea prepolymer/curative mixture ratio of betweenabout 1:0.75 to about 1:1.25. The DMA results of the IPNs were obtainedusing a TA Instruments 2980 unit, using the following parameters:tensile film mode; 20 μm amplitude; 1 Hz frequency; 10 cNm clampingforce; −100 to 250° C.; 3° C./min heating rate; and 15×6.5×0.6 (mm)sampling dimensions. The sample compositions are summarized below inTable 2 and the DMA results are summarized below in Table 3. TABLE 2Amount of Polyurea Prepolymer/Clearlink 1000 Amount of Urea AcrylateSample ID (%) (%)  0% IPN 100 0  10% IPN 90 10  20% IPN 80 20  30% IPN70 30  40% IPN 60 40 100% IPN 0 100

[0168] TABLE 3 Relative Relative Crosslink Crosslink DMA Tg density* DMATg DMA Tg density* (° C.) (1000 moles/cc) (° C.) (° C.) (1000 moles/cc)Thermal Thermal Before Radiation Radiation Sample ID Cure Cure RadiationCure Cure  0% IPN −44° C., 80° C. — −50° C., 71° C. −50° C., 73° C. — 10% IPN −47° C., 81° C. — −42° C., 70° C. −41° C., 74° C., — 120° C. 20% IPN −46° C., 72° C., — −48° C. −50° C., 72° C., 0.01387 135° C.104° C.  30% IPN −46° C., 72° C., 0.00358 −37° C., 43° C. −42° C., 70°C., 0.0243 131° C. 111° C.  40% IPN −46° C., 66° C., 0.0124 — −42° C.,66° C. 0.058 121° C. 100% IPN −50° C., 73° C. 0.83 — −42° C., 62° C.0.5588

What is claimed is:
 1. A method of forming a portion of a golf ballcomprising the steps of: providing at least a first polymeric componentand a second polymeric component, each polymeric component comprising atleast one monomer, oligomer, prepolymer, or a combination thereof;sufficiently polymerizing each polymeric component sequentially orsimultaneously to form a polymer or polymer network; crosslinking eachpolymer or polymer network to the other polymer or polymer network toform an interpenetrating polymer network (“IPN”); and forming the IPNinto the portion of the golf ball, wherein each polymeric component ofthe mixture is polymerized by exposing the mixture to at least oneenergy source, at least one initiator, or a combination thereof for atime sufficient to polymerize said polymeric component.
 2. The method ofclaim 1, wherein the at least one energy source is selected from thegroup consisting of microwave radiation, infrared radiation, visibleradiation, ultraviolet radiation, x-ray radiation, gamma radiation,electron beam radiation and a combination thereof.
 3. The method ofclaim 1, wherein the at least one initiator is selected from the groupconsisting of a thermal free radical initiator, a photoinitiator, acationic initiator, and a mixture thereof.
 4. The method of claim 3,wherein the thermal free radical initiator is selected from the groupconsisting of an azo compound, a peroxide, a persulfate, a redoxinitiator, and mixtures thereof.
 5. The method of claim 3, wherein thephotoinitiator is selected from the group consisting of a peroxide, anazo compound, quinine, benzophenone, nitroso compound, acyl halide,hydrazone, a mercapto compound, a pyrylium compound, a triacylimidazole,an organophosphorus compounds, a bisimidazole, a chloroalkyltriazine, abenzoate, a benzoyl compound, a benzoin ether, a benzil ketal, athioxanthone, an acetophenone derivative, a ketone, a metallocene, ahexafluorophosphate salt, a sulfonium salt, a diacrylate, a polyol, apyrollidone, and mixtures thereof.
 6. The method of claim 3, wherein thecationic initiator is selected from the group consisting of a Group IAorgano compound, Group IIA organo compound, aryl sulfonium salt,hexafluorometallic salt, Bronsted acid, Lewis acid, and mixturesthereof.
 7. The method of claim 1, wherein the initiator is present inan amount of greater than about 0.01 parts per hundred of total polymercomponent.
 8. The method of claim 7, wherein the initiator is present inan amount from about 0.01 to about 15 parts per hundred of total polymercomponent.
 9. The method of claim 7, wherein the initiator is present inan amount from about 0.1 to about 10 parts per hundred of total polymercomponent.
 10. The method of claim 1, wherein the polymerization of eachpolymeric component is subsequent or simultaneous with the crosslinkingof each polymer or polymer network to the other polymer or polymernetwork.
 11. The method of claim 1, wherein the first polymericcomponent is polymerized in the presence or absence of a secondpolymeric component to form a first polymer or first polymer network.12. The method of claim 11, wherein the at least a second polymericcomponent is polymerized in the presence of the first polymericcomponent or the first polymer or first polymer network to form a secondpolymer or second polymer network.
 13. The method of claim 12, whereincrosslinking of the first polymer or first polymer network to the secondpolymer or second polymer network occurs subsequently or simultaneouslywith the polymerization of the second polymeric component to form thesecond polymer or second polymer network.
 14. The method of claim 1,wherein the polymerization of each polymeric component and thecrosslinking of each polymer or polymer network to the other polymer orpolymer network occurs simultaneously to form an IPN.
 15. The method ofclaim 1, wherein the first polymeric component and the second polymericcomponent comprise monomeric, oligomeric or prepolymeric precursors ofvinyl resins; polyolefins; polyurethanes; polyureas; polyamides;polyamide/polyurethane copolymers, polyamide/polyurea copolymers,epoxy-end-capped polyurethanes, epoxy-end-capped polyureas,polyamide/polyurethane ionomers, polyamide/polyurea ionomers, acrylicresins; olefinic rubbers; polyphenylene oxide resins; polyesters; blendsof vulcanized, unvulcanized or non-vulcanizable rubbers withpolyethylene, polypropylene, polyacetal, nylon, polyesters, or celluloseesters; or polymers or copolymers possessing epoxy-containing, orpost-polymerization epoxy-functionalized repeat units.
 16. The method ofclaim 1, wherein the portion of the golf ball formed from the IPN is acore, intermediate layer or cover layer.
 17. The method of claim 1,further comprising providing a golf ball center; and disposing the IPNabout the center to provide a portion of the golf ball.
 18. The methodof claim 17, wherein the IPN is included in an intermediate layerdisposed about the center.
 19. The method of claim 17, wherein the IPNis included in a cover layer disposed about the center.
 20. A method offorming a portion of a golf ball comprising the steps of: providing afirst polymeric component comprising at least one monomer, oligomer,prepolymer, or a combination thereof; sufficiently polymerizing thefirst polymer component to form a first polymer or first polymernetwork; providing a second polymeric component comprising at least onemonomer, oligomer, prepolymer, or a combination thereof; sufficientlypolymerizing the second polymer component to form a second polymer orsecond polymer; and crosslinking the first polymer or first polymernetwork with the second polymer or second polymer network to form anIPN, wherein the first polymeric component is polymerized by exposingthe first polymeric component to a first energy source, a firstinitiator, or a combination thereof for a time sufficient to polymerizethe first polymeric component and the second polymeric component ispolymerized by exposing the second polymeric component to a secondenergy source, a second initiator, or a combination thereof for a timesufficient to polymerize the second polymeric component.